But some of the claims on cold exposure, brown fat and fat loss did pique my curiosity.

So I decided to do a bit of research and see what I could find.

Brown fat, also known as brown adipose tissue (BAT for short) is abundant in babies. The reason it’s brown is because it’s so tightly packed with mitochondria, which is where fat gets burned off.

The primary function of BAT is to generate heat. In fact, BAT is so metabolically active that just two ounces of the stuff can burn around 500 calories per day. BAT is normally inactive, just as long as you’re in your thermal comfort zone, which is part of the reason that it’s rarely detected and why BAT was traditionally thought to be irrelevant in adults.

However, more recent evidence suggests that its expression in adults is far more common than previously thought, with a higher likelihood of detection in women and leaner individuals [1].

Making yourself cold is supposed to “activate” BAT, which in turn generates heat, raises your metabolism and burns off regular fat.

The idea is that you take a cold shower for at least 30 seconds and let it run over your shoulders, neck and back. Research shows that this is the area where a lot of brown fat is found [2].

Many of the articles I came across cited a 2008 study as “proof” that taking cold showers for weight loss is a good idea [3]. When I looked at the study for myself, I was expecting to find two groups of people, one who had taken a cold shower every day for a few months, and another group that hadn’t. And the ones taking cold showers had lost the most weight.

The reality, however, was rather different.

Firstly, subjects in the study (11 lean men) spent an entire DAY in a respiration chamber, rather than taking a cold shower for a few minutes.

Mild cold exposure (60 F or 16 C) did increase the number of calories burned. In one of the subjects, there was an increase in daily energy expenditure of around 400 calories per day.

However, the average increase across all subjects was only 76 calories. This represents an increase in 24-hour energy expenditure of 2.8%.

So not only is the effect a relatively small one, it seems highly variable from person to person.

You might think that the increase in energy expenditure was caused by the men moving around more to keep themselves warm. But this wasn’t the case. In fact, mild cold exposure led to a significant drop in physical activity.

Although the researchers speculate that “regular cold exposure might be beneficial in body weight regulation,” they don’t give any recommendations about how long this cold exposure should last, or how cold you actually need to get.

Other research on the subject of cold exposure and fat metabolism shows that brown fat actually uses regular fat from the rest of the body to fuel itself [4].

For the study, subjects (6 healthy men with a BMI of 24-31) were kept cold, but not to the point of shivering, which itself will burn calories. Over a 3-hour period, their metabolic rates increased by roughly 80%, going from an average of 1.8 to 3.2 calories per minute. This was all from a few ounces of brown fat, which kept the men warm.

There was also a large variation in the amount of brown fat each subject stored, ranging from 31 to 329 milliliters. The more BAT a man had, the colder he could get before he began shivering.

Does this research offer any support for the idea that taking cold showers for weight loss is going to work?

Not really. To keep them cold, subjects in the study wore a liquid-conditioned tube suit, which had cold water poured into it.

There’s a big difference between having the whole of your body cooled for several hours and standing under a cold shower for 30 seconds. And even then the rise in metabolism was a relatively small one, averaging 1.4 additional calories burned for each minute of cold exposure.

Two hours of daily cold exposure has been shown to induce fat loss [7]. But the amount of fat lost – 1.5 pounds over a 6-week period – was small. And two hours of daily cold exposure is a lot different to 30 seconds spent in a cold shower.

There’s also some debate about the extent to which BAT is present in obese and overweight individuals.

In fact, some studies show lower BAT activity in people who are overweight or obese. The figure below, taken from this New England Journal of Medicine study, shows how BAT activity declines as body fat percentage increases.

It’s possible that lean adults may require increased metabolism in BAT for “non-shivering” thermogenesis to maintain body temperature when it gets cold. This isn’t so much of an issue for someone who is overweight or obese. Their fat acts as a layer of insulation to keep them warm.

Which brings me to another question.

Do thin people have high levels of brown fat to meet these thermogenic needs? Or are they thin because they have more active brown fat?

At this point, nobody knows for sure. But if you have a lot of fat to lose, a cold shower may be less effective for weight loss (assuming it’s effective at all) than it is for someone wanting to drop a few pounds to look good on the beach.

Some people are taking the idea of cold water immersion to the extreme, swimming in cold water in an attempt to raise their metabolic rate and lose weight more quickly.

The only problem here is that immersion in cold water appears to make you hungrier than normal, leading to an increase in calorie intake [5]. Researchers think that leptin and ghrelin (two hormones that play an important role in controlling your appetite) are to blame:

In summary, a short period of postexercise water immersion significantly increases ad libitum energy intake in the subsequent meal among young, trained men. This may be attributed, in part, to a tendency for lower levels of circulating leptin, together with higher active ghrelin after immersion in cold and neutral water, respectively.

So you might burn more calories by swimming in cold water… but end up replacing them all simply because the cold water makes you hungry.

There is some (highly speculative) research linking the rise in obesity with a parallel rise in the typical thermostat settings in US and UK homes [6]. But there’s no evidence to show that spending 30 seconds under a cold shower has any significant impact on your metabolic rate. I think that taking cold showers for weight loss is largely a waste of time and effort.

ABOUT CHRISTIAN FINN

Christian Finn holds a master's degree with distinction in exercise science, is a former personal trainer and has been featured on BBC TV and radio, as well as in Men's Health, Men's Fitness, Fit Pro, Zest, and Perfect Body magazine.